1. Technical Field
The present invention relates to an optical position detection apparatus and a display apparatus having a position detection function that is provided with the optical position detection apparatus.
2. Related Art
In an electronic appliance such as a portable phone, car navigation system, personal computer, ticket machine, bank terminal, or the like, a display apparatus having a position detection function, in which a touch panel is arranged on the front surface of an image generation apparatus such as a liquid crystal apparatus, has been used recently. In a display apparatus having the position detection function as described above, an input of information is performed while an image displayed on the image generation apparatus is referred to. The touch panel as described above is composed of a position detection apparatus for detecting the position of a target object in a detection area.
As detection types of the position detection apparatus, a resistive film type, an ultrasonic type, a capacitive type, an optical type, and the like, are known. The resistive film type is low-cost, but, like the capacitive type, has low transmissivity. The ultrasonic type or the capacitive type has a high response speed, but has a low environmental resistance. In contrast, the optical type has the characteristics of high environmental resistance, high transmissivity, and high response speed (see JP-A-2004-295644 and JP-A-2004-303172).
However, optical position detection apparatuses as described in JP-A-2004-295644 and JP-A-2004-303172 require light sources or light detectors near the display screen, the number of which corresponds to the resolution of position coordinates that should be detected, and thus are high-cost.
Accordingly, as schematically illustrated in FIGS. 10A and 10B, the inventor of the present invention is examining an optical position detection apparatus in which position detection light sources 12 are installed at end portions of a light guide plate 13 to face each other, and a light detector 15 detects a position detection light L2 that is emitted from the light guide plate 13 and reflected by a user's finger and so on. The optical position detection apparatus as described above has the advantages that it can detect the position of the finger and so on with a small number of position detection light sources 12 or light detectors 15 if there is a roughly linear relationship between the intensity of the position detection light L2 that is emitted from the light guide plate 13 and the distance from the position detection light source 12.
However, the optical position detection apparatus as illustrated in FIGS. 10A and 10B has a problem that when the position of the finger and so on is actually detected by the optical position detection apparatus, a large error may occur. As a result of examining the problem, the inventor of the present invention has newly found that such an error is caused by the scattering of the intensity distribution of the position detection light L2 in a detection area. That is, since in an area 13w that is spaced apart from the position detection light source 12 in a light guide plate 13, the position detection light L2 from the position detection light source 12 directly reaches the area 13w and the position detection light L2 that is reflected from an outer periphery side portion of the light guide plate 13 also reaches the area 13w, the light emission intensity of the position detection light L2 in the area 13w becomes high in comparison to other areas regardless of the fact that the area 13w is spaced apart from the position detection light source 12. In this case, the configuration as illustrated in FIGS. 10A and 10B is to explain the problem of the present invention, but does not refer to related art.